The unsatisfactory performance of public health systems, particularly in poor rural areas, has lead to calls for decentralization and greater community participation throughout the developing world. This project rigorously investigates where and why community health volunteers will be motivated to effectively carry out their assigned tasks. The project focuses on tuberculosis, a leading contributor to the global burden of disease, and proposes to use community volunteers as Directly Observed Treatment (DOT) providers to ensure that TB patients adhere to their extended treatment regimen. Social solidarity-the selfless willingness to help another without receiving direct benefits in return-is seen as the primary motivation for community volunteers when strict confidentiality must be maintained, as with TB case management. The new theory of solidarity formation that is developed indicates that spatially dispersed communities with less dense social networks will compensate for their limited ability to enforce cooperation among their members by investing in solidarity. The theory predicts that these communities should therefore produce more effective DOT providers. This hypothesis will be tested in a unique social laboratory in rural South India with a population of 1.2 million, covering 420 villages (neighborhoods) and including 50 kin-groups (sub-castes); kin-groups span a much larger area than the village and are an important source of economic and social support in the rural Indian context. Data will be collected from three sources. First, a randomized control trial will assign the 4000 adult pulmonary TB patients who enter the public health system over a 2.5-year period to one of four arms: (1) community DOT provider within the patient's kin-group in the same village; (2) community DOT provider within the patient's kin-group from a nearby village; (3) community DOT provider outside the patient's kin-group in the same village; (4) government DOT provider, the current method of care (control arm). DOT provider performance will be based on objective measures of treatment success as well as assessment of the patient's (and DOT provider's) experience. Second, a survey of 10,500 households will collect measures of solidarity using multiple techniques (questionnaire responses and experimental games). Third, historical census data on community spatial dispersion will be matched to TB patient outcomes and measures of community solidarity. Based on the theory, patients assigned to TB volunteers from their own kin-group are expected to enjoy relatively high levels of treatment success (Aim 1) and solidarity is expected to be greater within kin-groups than within villages (Aim 2). Looking across kin-groups, more spatially dispersed kin-groups are expected to generate better volunteer performance (conditional on the patient being assigned within kin-group) (Aim 3) and greater levels of solidarity (Aim 4). Given current efforts to decentralize the health system in India and other countries, research aiming to systematically evaluate successful community participation and understand its underlying preconditions comes at a particularly opportune time.